1,3-ELIMINATION REACTIONS OF (3,4-EPOXYBUTYL)STANNANES - APPROACH TO THE SYNTHESIS OF CYCLOEUDESMOL

The reactions that occur when stereochemically defined spirocyclic (3,4-epoxybutyl)stannanes are treated with C2H5AlCl2 depend critically on the relative orientation of tin, oxygen, and the three connecting atoms of carbon. A W arrangement of these atoms tends to favor formation of cyclopropanes by a concerted 1,3-elimination with inversion at both carbon centers. If this orientation cannot be achieved, cleavage of the epoxide occurs to give an ionic intermediate that can undergo a subsequent 1,3-elimination or a 1,2-shift of hydride promoted by an antiperiplanar carbon-tin bond.